Pyrotechnic charge and process for the preparation thereof

ABSTRACT

A pyrotechnic charge and a process for preparation thereof, whereby the pyrotechnic charge can be used as an impulse element requiring little space. The pyrotechnic charge has at least one nanostructured, porous fuel body; a protective layer on the surface of the at least one fuel body; and a fluorine-eliminating substance as an oxidizing agent, which is provided in the cavities or porosities of the at least one fuel.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a pyrotechnic charge having at least one nonstructured porous fuel body with a protective layer on the surface thereof, and with an oxidizing agent provided in the cavities of the body. Also disclosed is a process for the preparation of the inventive pyrotechnic charge.

2. Discussion of the Prior Art

A pyrotechnic charge or reactive material of that type and a process of preparation are described, for example, in DE 102 04 895 A1. The known reactive material consists of fuel bodies in the cavities of which, having a magnitude of 1-1000 nm, an oxidizing agent is introduced, and the surfaces of which are provided with a protective layer which can be broken open in order to induce the reaction between the fuel and the oxidizing agent. A fuel body according to this DE 102 04 895 A1 is defined in the context of the present invention as a nanostructured, porous fuel body.

The high reaction rate of this known reactive material is due to the very short distances or diffusion paths between the oxidizing agent (electron acceptor) and the fuel (electron donor, reducing agent), which are of the order of magnitude of less than 50 nm. In the case of the diffusion coefficients of 10⁻¹⁰-10⁻¹⁴ cm²s⁻¹ present here, such a great decrease in the diffusion path results in a considerable acceleration of the diffusion process as an important parameter influencing the reaction rate.

In the case of DE 102 04 895 A1, the fuel chosen is silicon, boron, aluminium, titanium or zirconium, while oxygen-releasing oxidizing agents based on ammonium, alkali metal and alkaline earth metal nitrates, perchlorates and peroxides are used. In the reaction between fuel and oxidizing agent, the high-boiling metal oxides stated in the table below thus form as reaction products. TABLE 1 Fuel Boron Aluminium Silicon Titanium Zirconium Metal B₂O₃ Al₂O₃ SiO₂ TiO₂ ZrO₂ oxide Phase at solid solid solid solid solid RT Boiling 2250° C. 3300° C. 2477° C. ˜2500° C. 4300° C. point

For this reason, the pressure-volume work of the reaction products as a basis for use of the reactive material, for example, in actuators is very greatly limited. Furthermore, the oxidic combustion products cannot undergo further exothermic reaction. Thus, for example in the case of oxygen-underbalanced explosives, use is made of the subsequent combustion of the resulting substances C and CO with the atmospheric oxygen in order to increase the vapour energy. However, this is not possible in the case of the oxide-based combustion products of the conventional reactive materials described here.

SUMMARY OF THE INVENTION

Starting from the prior art described above, it is the object of the present invention to further develop a pyrotechnic charge comprising a nanostructured, porous fuel body so that gaseous reaction products which themselves perform pressure-volume work form in the reaction between fuel and oxidizing agent.

This object is achieved by a pyrotechnic charge wherein the oxidizing agent is a fluorine-eliminating agent, and the provision of a process for the preparation of the pyrotechnic charge utilizing the oxidizing agent, which comprises a fluorine-eliminating substance. Advantageous developments and further developments of the invention are the subject of respective of the subclaims.

DETAILED DESCRIPTION OF THE INVENTION

The pyrotechnic charge of the invention has at least one nanostructured, porous fuel body, a protective layer on the surface of the at least one fuel body and an oxidizing agent which is provided in the cavities of the at least one fuel body. According to the present invention, a fluorine-eliminating substance is used as the oxidizing agent.

The nanostructured, porous fuel body corresponds to the fuel body defined in DE 102 04 895 A1. The disclosure content of DE 102 04 895 A1 is therefore fully incorporated by reference in this context. The advantage of the reaction of the fuel with a fluorine-eliminating substance as oxidizing agent is the formation of volatile fluids according to the equation $\begin{matrix} {M^{m} + {{{m/y} \cdot C_{x}}{F_{y}\overset{\Delta}{\longrightarrow}{MF}_{m{(g)}}}} + {{m/y} \cdot {xC}} + Q} & (1) \end{matrix}$

where m=maximum valency of the fuel M, which, in contrast to the abovementioned high-boiling metal oxides, are gaseous metal fluorides and therefore themselves perform pressure-volume work. Table 2 below shows, by way of example, the boiling points of some metal fluorides which can form as reaction products in the case of the pyrotechnic charge of the invention. TABLE 2 Fuel Boron Aluminium Silicon Titanium Zirconium Metal BF₃ AlF₃ SiF₄ TiF₄ ZrF₄ fluoride Phase at gaseous solid gaseous solid solid RT Boiling −99° C. 1272° C. −90° C. ˜284° C. 600° C. point subl. subl.

A comparison of the boiling points stated in table 2 for the metal fluorides formed as reaction products with the boiling points of high-boiling metal oxides as reaction products of the conventional reactive material, which boiling points are stated above in table 1, clearly shows the advantage of using a fluorine-eliminating substance as an oxidizing agent of the pyrotechnic charge of the present invention.

The oxidizing agent is preferably selected from the group consisting of fluorocarbons and fluoronitrogen compounds. In the case of the fluorocarbons as oxidizing agents, nanodisperse carbon, partly in the form of fullerenes and nanotubes, is liberated; this nanocarbon undergoes a strongly exothermic reaction with the atmospheric oxygen in an excellent manner during thermal excitation and thus increases the vapour energy in an advantageous manner. In the case of the fluoronitrogen compounds, the nitrogen liberated also increases the pressure-volume work of the corresponding systems.

In order to illustrate the pressure-volume work performed by the reaction products of the pyrotechnic charge of the present invention, the table below shows by way of example gas volumes V (in ml/mol) formed at 298 K for the following various fuel/oxidizing agent systems (2) to (6). 4n B+3(-C₂F₄-)_(n)→4n BF_(3(g))+6n C_((s))   (2) 4n Al+3(-C₂F₄-)_(n)→4n AlF_(3(g))+6n C_((s))   (3) n Si+(—C₂F₄-)_(n)→n SiF_(4(g))+2n C_((s))   (4) n Ti+(—C₂F₄-)_(n)→n TiF_(4(g))+2n C_((s))   (5) n Zr+(—C₂F₄-)_(n)→n ZrF_(4(g))+2n C_((s))   (6)

TABLE 3 System B/PTFE Al/PTFE Si/PTFE Ti/PTFE Zr/PTFE V [ml/mol] 89 655 89 655 22 414 22 414 22 414

Particularly suitable fluorine-eliminating oxidizing agents are those substances which can be introduced into the cavities of the nanostructured, porous fuel bodies by means of a thermally induced diffusion process, owing to the low melting points or boiling points. The fluorine-eliminating substances may also be soluble in fluid media which are capable of penetrating into the cavities of the nanostructured, porous fuel bodies. In particular, supercritical carbon dioxide CO_(2(scr)) is therefore used as a preferred solvent since it evaporates without leaving a residue on the one hand and reduces the risk of fire and explosion in the preparation process on the other hand.

Suitable fluorocarbons which can be incorporated into the cavities of the nanostructured, porous fuel bodies by thermally induced diffusion processes are, for example, the following compounds which, for the purpose of unambiguous identifiability, are classified with the numbers assigned by the Chemical Abstracts Service (CAS), in square brackets: octafluoronaphthalene (C_(10F) ₈) [313-72-4], decafluorobiphenyl (C₁₂F₁₀) [434-90-2], octakis(trifluoromethyl)cubane C₈(CF₃)₈ [50782-50-8], polyfluoro[60]fullerene C₆₀F₄₈ [160359-80-8], perfluorotridecane C₁₃F₂₈ [376-03-4], perfluorotetradecane C₁₄F₃₀ [307-62-0], perfluoropentadecane C₁₅F₃₂ [2264-03-1], perfluorohexadecane C₁₆F₃₄ [355-49-7], perfluoroeicosane C₂₀F₄₂ [37589-57-4] and perfluorotetracosane C₂₄F₅₀ [1766-41-2]. Fluorocarbons which can be incorporated in particular by solvent-induced diffusion are hexafluoropropene/vinylidene fluoride copolymers (Viton™) [9011-17-0], polychlorotrifluoro-ethylene [9002-83-9] (Kel-F™ waxes and oils) and polyvinylidene fluoride (PVDF) [24937-79-9].

Suitable fluoronitrogen compounds are, for example, poly(bisdifluoroaminoethylene) (—C₂H₂(NF₂)—)_(n) or complex compounds of perfluoroazonium cations and homologues thereof and transition metal fluoridate anions, such as, for example, [NF₄]₂[NiF₆]. The latter compounds are stable at room temperature, can be handled and permit very high fluorine storage densities.

The at least one fuel body of the pyrotechnic charge of the invention is preferably formed from silicon, boron, aluminium, titanium, zirconium or a mixture thereof.

The process according to the invention, for the preparation of a pyrotechnic charge comprises the steps of providing at least one nanostructured, porous fuel body, of providing the surface of the at least one fuel body with a protective layer and of providing the cavities of the at least one fuel body with an oxidizing agent. In addition, the process is characterized in that the oxidizing agent is a fluorine-eliminating substance.

The advantages of using a fluorine-eliminating substance as an oxidizing agent for a nanostructured, porous fuel body and preferred oxidizing agents of this type have already been explained in detail above, and these points will therefore not be listed again here.

As already mentioned the oxidizing agent can be introduced into the cavities of the at least one fuel body, for example, by thermally induced diffusion. Alternatively, it is also possible for the oxidizing agent to be introduced into the cavities of the at least one fuel body by solvent-induced diffusion, supercritical carbon dioxide CO₂ being preferably used as the solvent.

A further feature of the invention is the thermal pretreatment of the nanostructured, porous fuel bodies for the purpose of controlling the sensitivity and the reaction rate. It is known that fluorocarbon compounds, such as poly(tetrafluoroethylene), undergo a Grignard-like reaction with metals, such as magnesium, in the condensed phase with insertion of the metal into the C—F bond according to the following equation $\begin{matrix} {{nMg} + {\cdot {\left( {{{- C_{2}}F_{4}} -} \right)_{n}\overset{\Delta}{\longrightarrow}{n\left( {{- {CF}_{2}} - {{CF}({MgF})} -} \right)}_{n}}} + Q} & (7) \end{matrix}$

It has now been found that this Grignard reaction also takes place with the use of the fuels according to the invention. As a result of the controlled thermal pretreatment, the fuel (B, Al, Si, T, Zr) is functionalized with a monolayer of perfluorinated alkyl or aryl radicals and fluorine according to the following diagram. In this way, depending on duration and temperature of the pretreatment, the thermal sensitivity of the reactive materials can be reduced but at the same time the reaction rate thereof can be increased.

Thus, the fuel body comprising aluminium is heated, for example, with polytetrafluoroethylene to not more than 550° C., insertion of the aluminium into the C—F bond resulting. The reactive material thus produced can then be caused to detonate in a controlled manner, for example by electrothermal action.

The pyrotechnic charge according to the present invention, described above and defined in the attached claims, can be particularly advantageously used as an impulse element in which little installation space is available, such as, for example, for projectiles, for controlling the attitude of satellites, for controlling rockets, missiles, projectiles and the like, for igniting explosives or for igniting propellant charges, pyrotechnic charges and the like. 

1. Pyrotechnic charge, comprising at least one nanostructured, porous fuel body; and a protective layer on the surface of the at least one fuel body; and an oxidizing agent, which is provided in the cavities or porosities of the at least one fuel body, wherein the oxidizing agent is a fluorine-eliminating substance.
 2. Pyrotechnic charge according to claim 1, wherein the oxidizing agent is selected from the group consisting of fluorocarbons and fluoronitrogen compounds.
 3. Pyrotechnic charge according to claim 1, wherein the oxidizing agent is selected from the group consisting of octafluoronaphthalene (C₁₀F₈), decafluorobiphenyl (C₁₂F₁₀), octakis(trifluoromethyl)cubane C₈(CF₃)₈, polyfluoro[60]fullerene C₆₀F₄₈, perfluorotridecane C₁₃F₂₈, perfluorotetradecane C₁₄F₃₀, perfluoropentadecane C₁₅F₃₂, perfluorohexadecane C₁₆F₃₄, perfluoroeicosane C₂₀F₄₂ and perfluorotetracosane C₂₄F₅₀.
 4. Pyrotechnic charge according to claim 1, wherein the oxidizing agent is selected from the group consisting of hexafluoropropene/vinylidene fluoride copolymer, polychlorotrifluoroethylene and polyvinylidene fluoride.
 5. Pyrotechnic charge according to claim 1, wherein the oxidizing agent is poly(bisdifluoroaminoethylene) (—C₂H₂(NF₂)—)_(n).
 6. Pyrotechnic charge according to claim 1, wherein the oxidizing agent is selected from the group consisting of the complex compounds of perfluoroazonium cations and homologues thereof and transition metal fluoridate anions.
 7. Pyrotechnic charge according to claim 1, wherein the at least one fuel body is formed by a material selected from the group consisting of silicon, boron, aluminium, titanium, zirconium or a mixture thereof.
 8. Process for the preparation of a pyrotechnic charge, comprising the steps of: providing at least one nanostructured, porous fuel body imparting a protective layer to the surface of the at least one fuel body; and providing the cavities or porosities of the at least one fuel body with an oxidizing agent, wherein the oxidizing agent is a fluorine-eliminating substance.
 9. Process according to claim 8, wherein the oxidizing agent is selected from the group consisting of fluorocarbons and fluoronitrogen compounds.
 10. Process according to claim 8, wherein the oxidizing agent is selected from the group consisting of octafluoronaphthalene (C₁₀F₈), decafluorobiphenyl (C₁₂F₁₀), octakis-(trifluoromethyl)cubane C₈(CF₃)₈, polyfluoro[60]fullerene C₆₀F₄₈, perfluorotridecane C₁₃F₂₈, perfluorotetradecane C₁₄F₃₀, perfluoropentadecane C₁₅F₃₂, perfluorohexadecane C₁₆F₃₄, perfluoroeicosane C₂₀F₄₂ and perfluorotetracosane C₂₄F₅₀.
 11. Process according to claim 8, wherein the oxidizing agent is selected from the group consisting of hexafluoropropene/vinylidene fluoride copolymer, polychlorotrifluoroethylene and polyvinylidene fluoride.
 12. Process according to claim 8, wherein the oxidizing agent is poly(bisdifluoroaminoethylene) ( C₂H₂(NF₂)—)_(n).
 13. Process according to claim 8, wherein the oxidizing agent is selected from the group consisting of the complex compounds of perfluoroazonium cations and homologues thereof and transition metal fluoridate anions.
 14. Process according to claim 8, wherein the at least one fuel body is formed by a material selected from the group consisting of silicon, boron, aluminium, titanium, zirconium or a mixture thereof
 15. Process according to claim 8, wherein the oxidizing agent is introduced into the cavities of the at least one fuel body by thermally induced diffusion.
 16. Process according to claim 16, wherein the oxidizing agent is introduced into the cavities of the at least one fuel body by solvent-induced diffusion.
 17. Process according to claim 16, wherein the solvent is supercritical carbon dioxide CO₂.
 18. Process according to claim 8, wherein the surface of the at least one fuel body is functionalized with a monolayer of perfluorinated alkyl or aryl radicals and fluorine in order to provide the surface with a protective layer.
 19. Process according to claim 18, wherein the surface of the at least one fuel body is subjected to a thermal pretreatment under inert gas up to an initial exothermicity of the binary system in order to provide the surface with a protective layer.
 20. Use of the pyrotechnic charge according to claim 1 or of a pyrotechnic charge prepared by the process according to claim 8 as an impulse element for projectiles, for controlling the attitude of satellites, for controlling rockets, missiles, projectiles and the like, for igniting explosives or for igniting propellant charges, pyrotechnic charges and the like. 